Magnetorheological damper system

ABSTRACT

A magnetorheological damper system comprising a reservoir in communication with a damper. The damper comprises a damper cylinder defining a damper chamber, wherein the damper chamber contains a magnetorheological fluid and a movable damper piston. The damper piston comprises at least two coil windings on the outer surface of the damper piston, wherein the damper piston is capable of generating a magnetic field between the damper piston and a wall of the damper cylinder. The reservoir comprises a reservoir cylinder defining a passageway, wherein the reservoir includes a magnetorheological electromagnet capable of generating a magnetic field between the magnetorheological piston and a wall of the passageway. The combination of the an MR reservoir and MR damper leads to a damping system capable of damping a wide range of extreme forces.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 10/406,922, filed Apr. 4, 2003 now U.S. Pat. No. 6,953,108,which is hereby incorporated by reference.

REFERENCE TO GOVERNMENT

This invention was made with Government support under Contract Nos.DAAE07-00-C-L010 and DAAE07-01-C-L018 awarded by the United States Army.The Government has certain rights in this invention.

BACKGROUND OF THE INVENTION

One of the persistent design constraints in the field of engineering isvibration and/or force impact and/or fatigue management. That is, nearlyall engineered devices and systems must embody a design that issufficiently robust so as to safely survive all movement, vibration,impact, etc. that such a device or system is likely to encounter in itsuseful life. Examples of such areas of engineered devices and systemsare seismic protection devices, construction hardware, seating systemsin vehicles such as helicopters, boats, etc., manufacturing equipmentand the like, all of which relate to the present invention as will beself-evident from the text below that describes in detail variouspreferred embodiments.

Such design constraints, however, are no more self evident than in thefield of vehicle design. It is well understood that vehicles endure aconstant barrage of forces, impacts and vibrations throughout avehicle's entire useful life. Indeed, when it comes to vehicle design,it may be said that this adverse active environment is perhaps theprimary design constraint.

The common and long known methodology for meeting these rigorous designconstraints of vehicle design is the use of a spring and damper systemlocated at appropriate locations along the vehicle chassis, mostcommonly between each tire/wheel assembly and the vehicle frame. Themost common type of spring and damper system in this regard is theconventional shock absorber.

Conventional shock absorbers are comprised of two reciprocatingcylindrical tubes that extend, via an intervening spring, from thetire/wheel of the vehicle to the vehicle frame. One cylindrical tube isfilled with fluid and the other cylindrical tube houses a piston thatpasses through the fluid when the tubes move relative to each other.When the piston moves, it forces the fluid through restrictive passageswithin the piston. This thereby controls the speed with which the twotubes can move relative to each other for a given force.

When a vehicle encounters a hole or a bump, the tire/wheel moves inresponse thereto and thereby tends to urge the spring to either extendor compress. If there was a spring alone (i.e., no cylindrical tubesdiscussed above) between the tire/wheel and the frame, there is a riskthat this difficult terrain will cause the spring to resonate, acondition that adversely effects the handling and ride of the vehicle.The cylindrical tube structure, therefore, substantially inhibits suchresonating because movement of the spring is dependent on movement ofthe two reciprocating tubes. That is, the added resistance to movementof the tubes due to the restrictive flow of fluid resulting frommovement of the piston thereby dampens the forces that would otherwisecause the spring to extend or compress. This, in turn, substantiallyinhibits spring resonance and ensures proper handling and ride of thevehicle.

A number of modifications to this basic shock absorber design have beenmade over the years in order to enhance the damping effect of thedevice. For example, changing the size of the restrictive passages inone of the tubes and/or using a fluid with a different viscosity canhave material improved effects on the shock absorber performance.Performance characteristics can also be altered by increasing ordecreasing the size of the shock, changing the design of the tubes, theinternal valving (restrictive passages), etc.

There are, however, practical limits as to how much shock performancemay be changed by making such alterations. As a result, alternativedamping systems have been formulated.

One such alternative system is based on the utilization of a variableshear strength fluid such as a magnetorheological (MR) fluid. MR fluidbased devices are founded on the principle of controlling the shearstrength of the MR fluid by inducing and controlling a magnetic fieldaround the piston. Control of this magnetic field can change the shearstrength of the MR fluid anywhere from its normal state as a liquid toan energized state that is nearly a solid. Therefore, by precisioncontrol of the magnetic field, the shear strength of the MR fluid isadjusted so as to precisely control the damping performance of thedevice. An example of such an MR device is disclosed in U.S. Pat. No.6,419,058 which is hereby incorporated by reference in its entirety.

Nonetheless, the demands placed on vehicles, particularly off-roadvehicles (as well as other devices and systems that encounter a ruggedenvironment), continues to increase, all with the corresponding demandto avoid any degradation in passenger comfort or endurance. As a result,there is now an expectation and need to provide a damping system thatcan withstand very sizable range of operating environments, namely,anywhere from a flat, obstruction free surface to the most difficult ofoff-road conditions. Indeed, the system must not only withstand suchenvironments, but must operate effectively and continuously throughoutthis wide range of operating environments without degradation inperformance.

In this regard, the principle of using MR fluid appears to be wellsuited to providing the accurate control necessary for the operatingenvironment discussed above. However, the inventors are not aware of anyprior art MR devices capable of correctly operating at very high dampingforces and/or that support wide ranges of damping forces without thesystem either encountering undesired cavitation or without beingseverely damaged. Nor are the inventors aware of any prior art MRdevices that have adequate bandwidth for effective isolation of the highfrequency road inputs often encountered with difficult terrains.

OBJECTS AND SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide adamping device that addresses the known deficiencies in the prior art.

It is a further object of the present invention to provide a dampingdevice that operates correctly and efficiently at very high and very lowdamping forces.

It is a further object of the present invention to provide a dampingdevice that supports wide ranges of damping forces.

It is a further object of the present invention to provide a dampingdevice that has adequate bandwidth for effective isolation of the highfrequency road inputs.

It is yet a further object of the present invention to provide a controlsystem that effectively controls the damping device at very high andvery low damping forces.

It is yet a further object of the present invention to propose an MRdevice that operates according to the aforesaid objectives.

It is yet a further object of the present invention to provide an MRdevice that can be used on vehicles, seismic damping devices andnumerous other devices and systems that demand a damping system.

It is yet a further object of the present invention to propose an MRdevice that is relatively straightforward to manufacture and assemble.

These and other objects not specifically enumerated here arecontemplated by the vibration damping system of the present inventionwhich in one preferred embodiment may include a main housing having amagnetorheological damper valve movable within said main housing and areservoir chamber having a magnetorheological electromagnet and whereinthe main housing and said reservoir are in fluid communication with eachother with a magnetorheological fluid. The system further includes acontrol system which includes a routine for energizing saidmagnetorheological damper valve in response to at least one sensedcondition of said damping system so as to dampen forces exerted on saiddamping system. This routine includes a routine for also energizing saidmagnetorheological electromagnet in response to at least one sensedcondition of said damping system so as to substantially preventcavitation in said damping system over substantially the entireoperating range of said damper system.

In another exemplary embodiment of the present invention, there iscontemplated a method of damping forces that includes providing amagnetorheological (MR) damping system on a structure that encountersperiodic external forces. The damping system has a movable electromagnetand a stationary electromagnet, both of which being in fluidcommunication with magnetorheological fluid. The system senses at leastone external motion variable on said structure that causes movement ofsaid movable electromagnet. The system then energizes at least saidmovable electromagnet in response to said sensed external force. Thesystem will energize both said movable electromagnet and said stationaryelectromagnet when said sensed external motion variable exceeds apredetermined threshold amount such that cavitation of said dampingsystem is substantially prevented in said damping system beyond saidpredetermined threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforesaid object ands and summary are now discussed with referenceto specific exemplary embodiments of the present invention using theaccompanying drawing figures in which:

FIG. 1 is a perspective view of an exemplary embodiment of themagnetorheological damper system in accordance with the presentinvention;

FIG. 2 is a cross-sectional view of FIG. 1;

FIG. 3 is a cross-sectional view of an exemplary embodiment of themagnetorheological damper wherein the damper piston is compressed;

FIG. 4 is a cross-sectional view of another exemplary embodiment of themagnetorheological damper system in accordance with the presentinvention;

FIG. 5 is a perspective view of an exemplary embodiment of amagnetorheological damper piston;

FIG. 6 is a cross-sectional perspective view of FIG. 5;

FIG. 7 is a cross-sectional side of FIG. 5;

FIG. 8 is a side view of an another exemplary embodiment of amagnetorheological damper valve in accordance with the presentinvention;

FIG. 9 is a side view of yet another exemplary embodiment of amagnetorheological damper valve in accordance with the presentinvention;

FIG. 10 is a side view of one embodiment of a magnetorheological dampervalve in accordance with the present invention;

FIG. 11 is an enlarged cross-sectional view of FIG. 10 taken along lineA—A;

FIG. 12 is a side view of one embodiment of the internal wiper;

FIG. 13 is a top view of FIG. 12;

FIG. 14 is a perspective view of FIG. 12;

FIG. 15 is block diagram of a control system in accordance with onepreferred embodiment of the present invention;

FIG. 16 is a block diagram of a control system in accordance with asecond preferred embodiment of the present invention;

FIG. 17 is a block diagram of a control system for use in controllingthe damper system set forth in FIG. 2 in accordance with a preferredembodiment of the present invention;

FIG. 18 is a cross-sectional view of the use of an embodiment of thepresent invention in a vehicle; and

FIG. 19 is a perspective view of one-half of a mold used to polymer coatthe damper valve of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Discussed below is a detailed description of various illustratedembodiments of the present invention. This description is not meant tobe limiting but rather to illustrate the general principles of thepresent invention. It will be appreciated by the reader that theprinciples constituting the invention can be applied with great successto any number of applications that require management of shock forces,vibration, etc.

With reference to FIG. 1, an MR damper system 100 of the presentinvention is shown and includes a separate reservoir 101 component incommunication with a MR damper 102. However, the reservoir 101 may beintegral with the MR damper 102 as shown in FIG. 4 where the reservoir101 is depicted as being contained within the same structure of the MRdamper 102. As will be discussed in greater detail below, the reservoir101 serves to store and return MR fluid (not shown) that has beendisplaced from the MR damper 102 during compression of the damper 102and is particularly instrumental in achieving the objectives of thepresent invention.

Again referring to FIG. 1, reservoir 101 comprises a reservoir housing103 having two opposite ends which are sealed by a reservoir gland 104and an end cap (not shown), respectively. The reservoir gland 104 andthe end cap (not shown) are secured to the reservoir housing 103 viathreads on the inner diameter of the reservoir housing 103, however, thereservoir gland 104 and the end cap (not shown) can be friction fittedto the reservoir housing 103, or in certain circumstances, the end cap(not shown) can be integral with the reservoir housing 103 and thereservoir gland 104 can be coupled to the reservoir housing 103 in afriction-fit or screw-fit relation. It can also be coupled using coldforming of the reservoir housing 103 as well as by other methods knownto one of ordinary skill in the art.

The reservoir gland 104 includes a through-hole 105 that receives aconduit 106 which can be steel-braided tubing. The conduit 106 fluidlyconnects the reservoir 101 to the MR damper 102. In an exemplaryembodiment, conduit 106 is capable of handling at least 2000 psi ofpressure, although in other embodiments, the conduit 106 is capable ofhandling at least 3000 psi of pressure. As those skilled in the art willappreciate, different types of tubing having varying pressurecapabilities can also be used to place the reservoir 101 in fluidcommunication with the MR damper 102.

Continuing with reference to FIG. 1, the MR damper 102 includes a damperhousing 107 and a telescoping damper rod 108. At the ends of the damperhousing 107 and the damper rod 108 are a cylinder end 109 and a rod end110, respectively. The cylinder end 109 and the rod end 110 haveopenings 111, 112 that provide attachment points for the MR damper 102to a vehicle's chassis/body and suspension, respectively. As shown inFIG. 1, a bump stop 113, a bump stop cup 114, and rod end 110 areprovided at a second end of the damper rod 108. The bump stop 113 andthe bump stop cup 114 prevent damage to the damper housing 107 in theevent that an especially harsh force causes damper rod 108 to becomefully compressed.

The damper housing 107 of the MR damper 102 is sealed by a cylinder end109 at a first end and a damper gland 115 at a second end of the damperhousing 107 to define an internal chamber 219. The cylinder end 109 andthe damper gland 115 may be coupled to the damper housing 107 byscrew-fit or friction-fit. Alternatively, the cylinder 109 end is anintegral member of the damper housing 107 or can be screwed onto thedamper housing 107. In an exemplary embodiment, threads are located onboth the cylinder end 109 and the damper housing 107 so as to facilitatethe assembly and maintenance of the MR damper 102.

Referring next to FIG. 2, the internal configuration of the reservoir101 and the MR damper 102 is shown. In particular, the reservoir 101comprises a reservoir housing 103 that defines an internal chamber 215for holding a volume of MR fluid, preferably an amount equal to at leastthe volume of MR fluid that may be displaced by a fully compresseddamper piston 201 of the MR damper 102. An end cap 202 seals one end ofthe reservoir housing 103, which may be secured to the reservoir housing103 by a screw-fit, friction-fit, or may be integral with the reservoirhousing 103, all of which has been discussed previously as to othersimilar components of the system. As shown in FIG. 2, a gasket, or “O”ring 203, which is positioned on the outer circumference of the end cap202, seals the end cap 202 in the reservoir housing 103. The end cap 202is also provided with a valve 204 which allows for the introduction ofan inert gas such as nitrogen into the space 205 between the end cap 202and a reservoir piston 206. The purpose of introducing such an inert gasis discussed further below.

With further reference to FIG. 2, the reservoir piston 206 is generallycylindrical and is movable within the reservoir housing 103. Thereservoir piston 206 separates the inert gas from the MR fluid that mayenter the reservoir 101 from the MR damper 102. The reservoir piston 206is provided with two gaskets, 207, 208, to create a seal between thereservoir piston 206 and the walls of the reservoir housing 103.

The second end of the reservoir housing 103 is sealed with a reservoirgland 104. The reservoir gland 104 is a generally puck-shaped structurehaving a first face and a second face. The reservoir gland 104 alsoincludes first through-hole 209 and a second through-hole 105. Thereservoir gland 104 is also provided with a gasket 210 to create a sealbetween the reservoir gland 104 and the reservoir housing 103. The firstthrough-hole 209 is provided to allow the wires (not shown) thatcomprise the coil windings 218 of the reservoir electromagnet 212 toexit the reservoir 101 and is typically doped with a sealing substanceso as to sealingly retain the wire in place.

The second through-hole 105 allows MR fluid to either enter or exit thereservoir 101. The reservoir gland 104 also includes a recess 213 on thefirst face that is capable of receiving a bolt 214. The bolt 214 securesthe reservoir electromagnet 212 to the reservoir gland 104. The recess213 is positioned on the face of the reservoir gland 104 in order tocenter the reservoir electromagnet 212 within the internal space 215 ofthe reservoir 101, and thus concentrically within the cylindricalreservoir housing 103. That is, the reservoir electromagnet 212 ispositioned within the reservoir 101 so as to ensure the existence of asubstantially constant spacing between the outer circumference of thereservoir electromagnet 212 and the reservoir housing 103.

The reservoir electromagnet 212 is a generally cylindrical body having acentered through hole extending the length of the electromagnet 212. Thereservoir electromagnet 212 also includes a plurality of annularrecesses 216 provided on the outer diameter of the cylindrical body.Adjacent annular recesses define ribs 217 on the perimeter of thereservoir electromagnet 212. As illustrated in FIG. 2, the ribs 217 haveradiused outer edges. Alternatively, as illustrated in FIG. 9, the ribs217 may be substantially square. In yet another exemplary embodiment, asillustrated in FIG. 8, the ribs 217 of the reservoir electromagnet 212may be tapered.

A wire (not shown) is coiled about each annular recess 216 to form coilwindings 218. Adjacent coil windings 218 are wound in oppositedirections (as indicated by the arrows in FIG. 5) to generate a magneticflux emitted radially between adjacent ribs when a current is passedthrough the wire (not shown). In one exemplary embodiment, the reservoirelectromagnet 212 comprises at least two coil windings 218. In theexemplary embodiments depicted in FIGS. 2–4, the reservoir electromagnet212 includes four coil windings 218. As those skilled in the art willappreciate, the reservoir electromagnet 212 may have any number of coilwindings 218 depending upon the desired magnetic field.

As shown in FIG. 10, the coil windings 218 are slightly recessed betweenthe ribs 217 of the reservoir electromagnet 212. In an alternateembodiment, the circumference of the coil windings 218 and the walls ofthe reservoir electromagnet 212 may be substantially flush. The distancebetween the coil windings 218 and the wall of the reservoir housing 103as well as the distance between the outermost portion of the reservoirelectromagnet 212 and the wall of the reservoir housing 103 should besubstantially equal in order to promote laminar flow of the MR fluidover the reservoir electromagnet 212.

In one exemplary embodiment, the wire (not shown) that forms the coilwindings 218 is received in a small in-laid slot in each rib 217 so asto allow the wire to travel to the next adjacent recess 216. Thesein-laid slots are then filled with small piston gap plugs 227 to protectthe wire (not shown) spanning between adjacent annular recesses 216.Alternatively, as shown in FIG. 9, the wire (not shown) may be directedinto through-holes 900, 901 through the ribs 217 into each adjacentannular recess 216.

Turning now to the MR damper 102 itself, again with reference to FIG. 2,the MR damper 102 includes a damper housing 107 that defines an internalchamber 219. The internal chamber 219 houses a MR fluid and is bound bythe cylinder end 109 and a damper gland 115. According to one exemplaryembodiment, the MR fluid is a hydrocarbon-based fluid havingmicron-sized magnetizable particles suspended in the fluid. For example,in one exemplary embodiment, Lord Corporation MRF-122-2ED fluid may beutilized in the MR damper 102. In another exemplary embodiment, LordCorporation MRF 132AD fluid may be utilized in the MR damper 102. Asthose skilled in the art will appreciate, any MR fluid known ordeveloped in the art may be utilized in the MR damper 102 so long as theproperties of the MR fluid are accounted for in the control algorithmfor the MR damper systems 100.

A damper piston 201 is positioned within the internal chamber 219 of theMR damper 102 and includes piston end 220, a MR damper valve 223 coupledto a damper rod 108. The damper piston 201 is capable of moving withinthe internal chamber 219 along the longitudinal axis of the damperhousing 107. With reference to FIGS. 5 and 6, the piston end 220 is apuck-shaped structure having a centered through-hole 500, and aplurality of openings 221 positioned about the circumference of thepiston end 220.

The piston end 220 also includes a linear bushing 222 about the outerdiameter of the piston end 220. The piston end 220 is sized to centerthe MR damper valve 223 within the bore of the damper housing 107. Thatis, the piston end 220 ensures that the distance between the MR dampervalve 223 and the wall of the damper housing 107 is substantiallyconstant about the circumference of the MR damper valve 223. Accordingto one exemplary embodiment, the linear bushing 222 is made of steel. Inanother exemplary embodiment, the linear bushing 222 is made ofTeflon®-impregnated steel. At those skilled in the art will appreciate,the linear bushing 222 may be made from a plurality of materials suchas, but not limited to, aluminum, stainless steel, and titanium.

The MR damper valve 223 is a generally cylindrical body having aplurality of annular grooves 224 provided on the outer circumference.The annular grooves 224 are spaced apart forming ribs 225 betweenadjacent annular grooves 224. The annular grooves 224 and ribs 225correspond to the recesses 216 and ribs 217 of the reservoirelectromagnet 212. As with the reservoir electromagnet 212, the ribs 225on the MR damper valve 223 have radiused edges as shown in FIGS. 2–4.Alternatively, the ribs 225 may be squared as shown in FIG. 9. In yetanother exemplary embodiment of the MR damper valve 223, the ribs 225may be tapered (see FIG. 8).

Turning back to FIG. 2, a rebound stop 226 is positioned below the baseof the MR damper valve 223. The rebound stop 226 prevents damage to theMR damper valve 223 should the damper rod 108 extend to the point wherethe MR damper valve 223 nearly contacts the damper gland 115. Accordingto one exemplary embodiment, the MR damper valve 223 is made of steel.In another exemplary embodiment, the MR damper valve 223 is made fromheat-treated steel. As those skilled in the art will appreciate, the MRdamper valve 223 may be made from any material having direct currentmagnetic properties.

The annular grooves 224 on the MR damper valve 223 are sized to allowfor a wire (not shown) to be wound within each annular recess 224 toform a coil winding (not shown) or a electromagnet. The wire and coilwindings are not shown in FIG. 2 for purposes of clarity in thedrawings, but the wire and coil windings 300 are illustrated in FIG. 3.The coil windings (not shown) of each individual annular recess 224 arewound in opposite directions so that the magnetic field generated byeach coil winding (not shown) passes through the fluid gap, into thedamper housing, back into the fluid gap, and into an adjacent magneticpole. Accordingly, as the MR fluid moves through the openings 221 on thepiston end 220 and past the MR damper valve 223, an electrical currentmay be passed through the wire to create a magnetic field. The magneticfield alters the shear strength of the MR fluid passing between the ribs225 and the damper housing 107. As discussed previously with respect tothe reservoir electromagnet 212, gap plugs 227 protect the wire (notshown) as it spans between adjacent annular grooves 224. Alternatively,as shown in FIG. 9, the ribs 225 of the MR damper valve 223 may beprovided with through-holes 900, 901 that allow the wire (not shown) tospan adjacent annular grooves.

Turning to FIGS. 3, 4, and 11, the coil windings 300 are also protectedby a coating 301. The coating 301 can be a polymer or an epoxy coating.As those skilled in the art will appreciate, other polymers coatingsknown or developed in the art may be utilized to encapsulate the coilwindings 300. The number of coil windings 300 and the thickness of thecoating 301 are sized to promote laminar flow of the MR fluid along theouter surface of the MR damper valve 223. That is, the coated coilwindings 300 are to have substantially the same circumference as the MRdamper valve 223.

As shown in FIGS. 2–4, a piston bolt 228 secures the piston end 220 andthe MR damper valve 223 to the damper rod 108. In the embodimentsdepicted in FIGS. 2–4, the piston bolt 228 is secured to the damper rod108 via threads on the outer diameter of the piston bolt 228 and threadson the inner diameter of the damper rod 108. In another exemplaryembodiment, the damper rod 108 may be secured to the piston bolt 228 bya friction fit. As shown in FIGS. 2–4, the damper rod 108 is a generallycylindrical member having an inner bore. Wires from the coil windings300 are threaded through the damper rod 108 and exit the rod end 110 toa power supply (not shown).

In one embodiment, a thermocouple or a thermistor (not shown) isdisposed on the end of the piston bolt 228 or the piston end 220 so thatthe temperature of the MR fluid actually present in the chamber may bedetermined. Since temperature is one condition that dictates theoperation of the electromagnets in the system since the properties of MRfluid change with temperature, the presence of the temperature sensorwithin the system itself ensures accuracy and precision in the operationof the system.

The rod end 110 is coupled to the damper rod 108 by a press-fit,screw-fit, or friction-fit relation. As shown in FIGS. 5–7, the rod end110 has a generally circular head 229 integral with a cylindrical body230 having a main bore 231 extending along the longitudinal axis of thecylindrical body 230. A through-hole 502 perpendicular to the main bore231 of the rod end 110 permits the wires (not shown) from the coilwindings 300 to exit the MR damper 102. The circular head 229 of the rodend 110 is provided with an opening 112 that is adapted to couple to therod end 110 to the suspension (not shown) of the vehicle.

Turning back to FIGS. 2–3, at the other end of the damper housing 107, adamper gland 115 seals the damper housing 107. According to an exemplaryembodiment depicted in FIG. 2, the damper gland 115 is screwed onto thedamper housing 107 and sealed by at least one gasket 233. The dampergland 115 is provided with a centered opening 234 for the damper rod 108to move through. A generally circular recess 235 or counterbore isprovided on the internal face of the damper gland 115. Within the recess235 is placed an internal wiper 236.

With reference to FIGS. 12 and 13, the internal wiper 236 is a generallyflat annular disc having a centered opening 1200 that is sized to fitwith very tight tolerance on the outer surface of the damper rod 108.The opening 1200 of the internal wiper 236 is characterized by a bevelededge 1201 as shown in FIG. 12. As also shown in FIG. 12, the side of thewiper 236 opposite the beveled edge also has a slight taper. As thoseskilled in the art will appreciate, the internal wiper 236 may be madefrom a plurality of materials such as, but not limited to, brass, steel,titanium, aluminum, metallic alloys, and composite materials.

As a result of the tight tolerance between the centered opening 1200 andthe outer surface of the damper rod 108, the internal wiper 236functions to remove or “wipe” MR fluid from the damper rod 108 as thedamper rod 108 moves in a direction away from the damper housing 107. Inother words, as the damper rod 108 moves past the internal wiper 236,the MR fluid that may have adhered to damper rod 108 is wiped away fromthe damper rod 108 and thereby prevented from inducing excessive wear onthe seal due to the momentum and abrasiveness of the MR fluid.

Turning to another exemplary embodiment, reference is now made to FIG.4. The embodiment depicted in FIG. 4 is similar to the MR damper system100 that is illustrated in FIG. 2 with the exception that the reservoir101 and the MR damper 102 are integral in one cylindrical structure 400.In this regard, the reservoir 101 and the MR damper 102 are incommunication by a through-hole 401 positioned on the reservoir gland402. The reservoir 101 comprises a reservoir electromagnet 212 securedto the reservoir gland 402 by a bolt 214 and includes a reservoir piston206 that sealingly engages the cylindrical walls by gaskets 207, 208.

The reservoir piston 206 divides the reservoir 101 into two areas 205,215. In the first area 205 of the reservoir 101, an inert gas such as,but not limited to, nitrogen, may be introduced therein by a valve 403positioned on the cylinder end 109. The second area 215 of the reservoir101 is sized to hold a volume of MR fluid that may be displaced from theinternal chamber 219 of the MR damper 102 as a result of movement of thepiston 201.

The internal chamber 219 of the MR damper 113 is defined by thecylindrical wall 400, the reservoir damper gland 402, and the MR dampergland 115. Within the internal chamber 219 is a MR fluid and a MR damperpiston 201. The damper piston 201 comprises a piston end 220 coupled toa MR damper valve 223 and a damper rod 108. The MR damper valve 223comprises a plurality of coil windings 300 which can generate a magneticfield when a current is passed through the coil windings 300. When amagnetic field is generated, the shear strength of the MR fluid thatflows over the MR damper valve 223 increases. Consequently, the forcerequired to move the damper piston 201 through the MR fluid alsoincreases.

As shown in FIG. 3, a rebound stop 226 is positioned below the MR dampervalve 223 to prevent damage to the MR damper valve 223 or the dampergland 115 in the event that the damper rod 108 is fully extended. Aninternal wiper 236 is also positioned within the damper gland 115, andthe internal wiper 236 functions to remove MR fluid that may “adhere” tothe damper rod 108. The damper rod 108 also includes a rod end 110 andmay optionally include a bump stop 113 and a bump stop cup 114.

MR Damper System Control and Operation

Turning next to the control and operation of a MR damper system inaccordance with the present invention, reference is made to FIGS. 15 and16 wherein two alternative approaches to system control are depicted.The first, FIG. 15, is based on a closed loop control approach. Thesecond, FIG. 16, is based on an open loop control approach. In thisregard, the control scheme depicted in these figures is directed tocontrol of a MR damper valve 223 in a generic sense. That is, thesefigures do not explicitly identify a control scheme for simultaneouscontrol of a MR damper valve 223 and a reservoir electromagnet 212 assuch structure is described in exemplary embodiments described above. Asystem for such simultaneous control is more affirmatively identified inFIG. 17, which will be discussed in greater detail below.

With reference first to FIG. 15, the closed loop control system offers achoice of control algorithms 1502, 1503 to the user which are selectedby activation of a switch 1504. Switch 1504 can be a mechanical switch,adjusted by a vehicle occupant or operator. Alternatively, the switchcan take the form of a subroutine within the control system that servesto evaluate the operating conditions of the structure being dampened andthen serves to automatically select the most appropriate controlalgorithm 1502, 1503 for those conditions. The selection of an algorithmshall depend on the desire of the user or on the programming of aselection subroutine of the control system. For example, one algorithmmay be particularly well suited for a particularly treacherous off-roadterrain. Another algorithm may be better suited for a relatively flatand smooth terrain. Alternatively, one algorithm may be designed toensure the vehicle maintain certain ride characteristics no matter whatthe nature of the terrain. In one exemplary embodiment, the user orsoftware may choose a control algorithm known to those in the art as a“skyhook” algorithm.

The choice of the algorithm will then dictate to the system the desireddamper force 1508 depending on various inputs used in the algorithm thatare received in the closed loop control 1506. The inputs to the closedcontrol loop include the damper system temperature 1518, i.e., thetemperature of the MR fluid, the damper speed 1520, i.e., the speed withwhich the damper rod 108 is actuated upon encountering an obstacle orhole, and the actual damper force 1522. The methods by which each ofthese inputs is obtained will be appreciated as being known to those ofordinary skill in the art. For example, the temperature of the MR fluidcan be obtained with a thermocouple.

Based on the inputs 1518, 1520, 1522 received by the closed loop control1506 and governed by the selected algorithm, the control 1506 generatesa damper current command 1510 (so long as the inputs indicate a signalis needed) and delivers it to a high bandwidth transconductanceamplifier 1512 (discussed in greater detail below). The amplifier 1512then amplifies the signal into an electrical current 1513 that isapplied to the electromagnet (the coils) 1514 of the damper system 1516.This causes the shear strength of the MR fluid to change in directproportion to the magnitude of the electrical current 1513 and thusdampens the movement of the MR damper piston 201 with the system 1516 ina manner that is directly responsive to the actual inputs 1518, 1520,1522. Like all closed loop systems, this system automatically andcontinually adjusts the electrical current 1513 applied to the coilsuntil the actual damper force 1522 matches the desired damper force 1508of the algorithm.

Turning then to FIG. 16, the open loop control system in accordance withthe present invention is now described. In this regard, as with theclosed loop system, the user chooses a desired algorithm, 1602, 1603according to activation of an algorithm switch 1604. The selection of analgorithm is based on the desire of the user as discussed above.

As with the closed loop system, the choice of the algorithm will thendictate to the damper specific lookup table 1606 the desired damperforce 1608 depending on various inputs used in the algorithm. A deriveddamper current command 1610 for any given set of parameters isidentified from the “Damper-Specific Look Up Table” 1606. This look uptable 1606 contains data that is based on the characteristics of anactual damper system that conforms to the system that is beingcontrolled. In other words, the look up table is created based onperformance data that is obtained from an actual damper system havingthe same design as the damper unit being controlled by the look uptable. This “actual” data serves to generally “characterize” theoperation of any damper system that is similarly (or identically)designed and therefore this data can be used as general control data forall such damper systems.

In operation, the damper-specific look up table receives a velocityfeedback input 1620 and a temperature feedback input 1618 (i.e.,temperature of the MR fluid) in addition to the desired damper force asdetermined by the algorithm. Based on the values of each of theseinputs, the system will refer to a look up table that contains theappropriate damper current command so that the damper matches thedesired damper force based on the characterized actual damper. In otherwords, this damper current command is the value that was deemed mostappropriate for the same given inputs on a prototypical damper systemthat was used to generate the look up table. The damper current command1610 is then communicated to the high bandwidth transconductanceamplifier 1612 (discussed in greater detail below) which amplifies thesignal into an electrical current 1613. The current 1613 is then appliedto the electromagnet (i.e., the coils) 1614 of the damper system 1616 tothus change the shear strength of the MR fluid for the purposesdiscussed above.

Some having ordinary skill in the art perhaps may take the position thatthe closed loop system discussed with reference to FIG. 15 providesslightly more accurate damping control than the open loop systemdiscussed with reference to FIG. 16. This may be based on the ability ofa closed loop system to constantly monitor the force feedback data fromthe damper and to thereby finely adjust the current command to the MRdamper system 100. However, closed loop systems of this type typicallyrequire complex or at least expensive feedback devices (e.g., loadcells, etc.) and more powerful computing devices, i.e. a fastermicroprocessor, that are not otherwise necessary in an open loop system.Thus for the sake of simplicity and cost, there is perhaps at least aneconomic incentive to control the MR damper 102 using an open loopsystem (i.e., use a look up table) as referenced in FIG. 16. It will beappreciated by those of ordinary skill in the art that either type ofsystem is contemplated as being part of the present invention.

As a final point regarding the control systems of FIGS. 15 and 16, it isnoted that both systems utilize a high bandwidth transconductanceamplifier 1512, 1612. Given the advantages this amplifier adds to thecontrol system, a brief discussion regarding its operation is useful.

In this regard, it will be understood that typically a damper currentcontrol command is a low level signal (preferably a voltage signal butit can also be serial digital, parallel digital, fiber optic or otherknown means of transmitting data) that must be converted and amplifiedinto a current output of sufficient magnitude to drive the MR systemelectromagnet windings 1514, 1614. It will also be appreciated that isvery desirable in the context of the present invention to exercise highbandwidth control of the MR damper valve 223 and the reservoirelectromagnet 212 so as to maximize the dynamic performance of thesystem. However, the windings 218, 300 on each of these components havesignificant electrical inductance by virtue of their need to generatelarge damping forces, such large damping forces being achieved bymagnetizing the MR fluid in the gaps between the ribs 217, 225 andhousing 103, 107. This high inductance makes generation of a currentoutput of sufficient quality to achieve high bandwidth from a low levelsignal control virtually impossible without a current amplifier of sometype.

It is to address these competing interests that the high bandwidthtransconductance amplifier in accordance with the present invention isused. In this regard, the present invention contemplates the use of ahysteretic switchmode transconductance amplifier, i.e., atransconductance amplifier that utilizes a hysteretic switchingtechnique as opposed to fixed frequency switching. Such a hystereticswitching technique ties the switching frequency and duty cycle of theamplifier to the proportion of error between the desired and measuredcurrent through the coil windings 218, 300 as opposed to a set fixedfrequency. In addition, this type of amplifier incorporates a DC/DCconverter that increases the voltage that can be supplied to the damperfrom, say 12 VDC to 60 VDC to further improve transient response of thesystem. However, operation of the high bandwidth transconductanceamplifier is still possible without such a supplemental DC/DC converter.

Through the use of a high voltage input and the hysteretic switchingtechnique, the problems otherwise encountered due to the high inductancewindings to inhibit high bandwidth control are substantially reduced oreven eliminated. For example, the use of a high voltage input gives theamplifier greater capability to generate larger magnitudes of currentflowing through the coils 218, 300, and to do so at an increased speed,over amplifiers using a low voltage input.

The amplifier, known by those familiar with the art as a hystereticcurrent mode converter, oscillates at a variable frequency betweenconduction and regeneration. It is the ratio of time spent in conductionto regeneration that defines how much current flows through the coilwindings. If more coil current is desired by the control system, theamplifier output stage spends a greater proportion of its time in theconduction phase. If less coil current is desired by the control system,the amplifier output stage spends a greater proportion of its time inthe regeneration phase. Because of the large inherent inductance in thecoil winding, the amplifier behaves as a synchronous flyback converter,generating voltage potentials greater than the supply voltage. In thiscase, energy stored in the coil winding inductor may be increased involtage by the amplifier, and returned to the amplifier power supply,presumably to be used to re-energize the coil winding at a later time.

This allows any energy stored in the winding to be recovered rather thandissipated and facilitates very fast reductions in coil current.Finally, the hysteretic switching technique can approach zero (i.e., itcan momentarily apply direct current to the coil winding) when the errorbetween the desired and actual current is large. As a result, heatgeneration within the semiconductor switches is minimized when thecurrents involved are large. Each of these advantages is extremelyconducive to the amplifier achieving the high system bandwidth that isdesired.

As a last statement regarding the amplifier, it is noted that in apreferred embodiment, the hysteretic switchmode transconductanceamplifier is implemented using an electrical circuit designed with acommercially available HIP4080A integrated circuit from Intersil. Ofcourse, other electronic designs that support hysteretic control arealso known to those of skill in the art.

As a final discussion regarding a control system in accordance with thepresent invention, reference is next made to FIG. 17 which graphicallydepicts a system for controlling the damper system 100 of FIG. 2. Inthis regard, a dedicated hysteretic transconductance amplifier 1708,1710 is provided for the MR damper 102 and the MR reservoir 101. It isalso seen that the MR damper 102 includes sensors providing-MR fluidtemperature feedback 1704 and velocity feedback 1706, i.e., feedback onthe velocity of the suspension system as it encounters an obstacle.

Within the controller (not shown), there is stored the control algorithm1602 (or choice of algorithms as discussed above) along with two sets oflookup tables, namely a damper set of lookup tables 1702 and a reservoirset of lookup tables 1700. Each lookup table contains current commanddata that is organized according to both velocity values for thesuspension system and desired forces for each velocity value. In otherwords, for each value of velocity and for each value of a desired force,there is a value corresponding to current demand.

The control algorithm 1602 determines the value of the desired force fora measured velocity which thereby leads to the controller issuing thenecessary current command. In the case of the damper set of lookuptables 1702, the controller issues a damper current command 1712 and inthe case of the reservoir set of lookup tables 1700, the controllerissues a reservoir current command 1714. It should be noted in thisregard, however, that the only time a reservoir current command 1714 isissued is when the velocity is a positive value, i.e., when the damperrod 108 is being pushed into the damper housing 107. There is noreservoir current command value when the velocity value is negative,that is, when the damper rod 108 is extending away from the damperhousing 107. The reasons for this will become more apparent in thedescription of the operation of the damper system 100 set forth below.Furthermore in this regard, although a preferred embodiment describedherein contemplates a damping system that uses a reservoir valve, theprinciples of the control system described herein are equally applicableto a damping system that does not use a reservoir valve. In such aninstance, for example, there would be lookup tables for the dampingsystem alone.

In operation, the controller monitors the velocity of the suspensionsystem and the temperature of the MR fluid within the damper system. Themeasured temperature will dictate which of the damper set of lookuptables 1702 and which of the reservoir lookup tables 1700 to utilize.The selected algorithm will then identify the desired damper force,which is then translated by the look up table to an appropriate currentcommand 1712 and the appropriate reservoir current command 1714(assuming the velocity value is positive) from the lookup tables 1700,1702, and will then send each of these respective signals to theamplifier 1708, 1710 dedicated to the MR damper 102 and the MR reservoir101, respectively. Each amplifier 1708, 1710 will then convert thesignals to current and energize the windings (coils) 300, 218 of itsrespective electromagnet 223, 212. The energization of these coils 300,218 will then lead to the enhanced damping effect of the MR dampingsystem 100 of the present invention for the encountered force.

In view of the foregoing, it is now useful to provide an example of theactual operation of a damping system 100 in accordance with the presentinvention. Although this description is directed towards a damper 102used on a vehicle 1800, it will be readily apparent to those in the artthat the present invention has a wide variety of applications. In thisregard, reference is made to FIG. 2 and FIG. 18 where the structure ofFIG. 2 is shown mounted on an actual vehicle 1800.

In this example, it is assumed that the control algorithm is one thatmimics a traditional passive damper, i.e., it mimics a device where thedamping force is proportional to the differential speed between thedamper rod 108 and the damper housing 107. Of course, there arealgorithms that offer far more sophisticated control than the systemjust described, however, for the purposes of this example a simplealgorithm shall suffice.

Referring to FIG. 18, a vehicle 1800 is shown having mounted thereon theMR damper 102 and reservoir 101. Surrounding the MR damper is a spring1804 to provide a spring/damper pair that serves to introduce compliancebetween the vehicle chassis 1808 and the wheel/tire 1810. There are alsosensors mounted on the vehicle, namely, an accelerometer 1814 formeasuring wheel/tire acceleration, accelerometer 1816 for measuring thesprung mass acceleration, and position sensor 1812 for measuringsuspension position. Finally, the vehicle 1800 also supports amicroprocessor-based software controller 1818 and the previouslydescribed hysteretic transconductance amplifier 1820 along with itsDC/DC low to high voltage converter 1822. It will be understood that thesensors and the amplifier and other electronics are all connected to themicroprocessor.

At all times the controller 1818 monitors the sensors. In this example,the controller 1818 computes the velocity of the suspension bydifferentiating the signal received from the position sensor 1812 andbases its damper force signal thereon.

As the wheel/tire 1810 of the vehicle 1800 encounters an obstacle 1802,the wheel/tire 1810 is forced to move upwardly thereby causing thespring/damper pair to compress rapidly. The controller 1818differentiates the signal from the position sensor 1812 to arrive at asuspension velocity. The control algorithm then reacts to the suspensionvelocity signal by referring to the lookup table (See FIG. 17) for boththe MR damper 102 and the MR reservoir 101 and selecting the dampercurrent command 1713 and reservoir current command 1714 that correspondsto the MR fluid temperature and the desired reactive force for thatvelocity signal under that algorithm. The amplifier 1820 draws powerfrom the DC/DC converter 1822 and quickly energizes the coils 300 of theMR damper valve 223 and the coils 218 of the reservoir electromagnet 212to the current level dictated by the corresponding damper currentcommand 1713 and reservoir current command 1714, respectively.

From a mechanical point of view, the damper rod 108 is at this timebeing driven upwardly into the damper housing 107 and is thereby causingMR fluid to flow over the MR damper valve 223. This flow of MR fluidcauses a differential pressure across the damper valve 223 which itselfopposes the upward movement of the damper rod 108. However, additionalresistance is introduced due to the increased shear strength of the MRfluid resulting from the magnetic flux now found in the coils 300.

In the event the controller commands that more current be supplied tothe coils 300 of the MR damper valve 223, the magnetic field between theMR damper valve 223 and the wall of the damper housing 107 increases.This increase of course in turn increases the shear strength of the MRfluid which manifests itself as yet greater increased damping forceopposing the direction of travel of the damper rod 108.

However, further explanation is still required to illuminate thefunction and utility of exciting the coils 218 in the reservoirelectromagnet 212. In this regard, it is useful to discuss the flow offluid between the MR damper 102 and the reservoir 101 and the fluiddynamics that can arise in certain circumstances.

As the damper rod 108 moves into the damper housing 107, the volume inthe damper housing 107 available for holding the MR fluid is decreasedexactly by the volume that the damper rod 108 displaces in the damperhousing 107. Since MR fluid is essentially incompressible, it is forcedto travel from the damper housing 107 to the reservoir 101 through theconduit 106. Once in the reservoir 101, the MR fluid flows over thereservoir electromagnet 212 into the internal space 215 of the reservoir101. As flow continues and pressure builds within the reservoir, thereservoir piston 206 will be displaced by a volume equal to the volumeof the damper rod 108 that enters the damper housing 107. The gas, e.g.,nitrogen, present in the space 19 behind the reservoir piston 206 then,of course, compresses and serves to enhance the dampening effect of thesystem.

In instances where the velocity of the damper rod 108 into the damperhousing 107 are especially dramatic and thus result in large controllerdemands on the coil 300 of the MR damper 102, there is a need to preventthe risk of cavitation, i.e., the creation of a low pressure vaporbubble, of the MR fluid in the low pressure side of the MR damper valve223 (referred to previously). That is, in order to create the dampingforces necessary to counteract a dramatic velocity change in thesuspension, high current must be passed through the coils 300 of the MRdamper valve 223. This high current obviously dramatically increases theshear strength of the MR fluid. As a result, a corresponding dramaticincrease in the pressure differential across the MR damper valve 223 iscreated. This leads to a very high pressure being present on the side ofthe MR damper valve 223 furthest from the damper rod 108 and potentiallya very low pressure being present on the side of the MR damper valve 223nearest the damper rod 108.

When this low pressure on the side of the MR damper valve 223 nearestthe damper rod 108 approaches the vapor pressure of the MR fluid, thereis the possibility that a vapor bubble is created. When such a bubble iscreated, the damping system no longer can generate damping forces fromthe effect of differential pressure and instead of the reservoirreceiving only that volume of fluid corresponding to the displacedvolume of the damping rod 108, the entire volume of fluid swept by theMR damper valve 223 is urged into the reservoir 101. Clearly this is anunacceptable condition and it is primarily for this reason that thepresent invention contemplates the energization of coils 218 in thereservoir electromagnet 212.

It is known in the art that creating an increase in the pressure in thespace 205 containing the compressible fluid, e.g., nitrogen, of thereservoir 101; serves to create an increased “precharge” pressure withinthe entire damping system 100, including in the space behind the MRdamper valve 223 nearest the damper rod 108. With the existence of anincreased pre-charge pressure in this area, the damping system 100 isable to endure greater differential pressure between opposing sides ofthe MR damper valve 223 without cavitation. However, increasing thepre-charge pressure in this manner also increases the parasitic springrate of the system and generally limits the effectiveness and quality ofthe damping system.

Accordingly, the present invention utilizes the reservoir electromagnet212 to increase the so called “pre-charge” pressure in the system butonly in response to the detection of certain large damper force valuesthat may otherwise induce cavitation. In all other respects, thepre-charge pressure will remain as determined by the pressure in thespace 205 of the reservoir 101. In other words, when large damper forcevalues are encountered, the control system energizes both the coils 300,218 of the MR damper valve 223 and the reservoir electromagnet 212 (inthe manner described with reference to FIG. 17), the former to createthe differential forces necessary to respond to the velocity signal, thelatter to increase the “pre-charge” of the damper system 100 and therebyprevent cavitation. In this fashion, the present invention has thecapability to effectively and qualitatively dampen both “normal” anddramatic forces while also avoiding undesirable parasitic spring forces.

Fabrication

According to the teachings of the present invention, the MR damper valve223 and the reservoir electromagnet 212 may be fabricated by variousmethods. Generally, the reservoir electromagnet 212 and the MR dampervalve 223 are fabricated by similar methods but the description to thesevarious fabrication methods will be directed to the MR damper valve 223.The MR damper valve 223 may be manufactured from steel or othermagnetizable metals. Annular grooves 224 are then machined along theouter diameter of the MR damper valve 223. According to one exemplarymethod, the annular grooves 224 are tapered as shown in FIG. 8.According to one exemplary method, the edges of the annular grooves 224may be radiused as shown in FIGS. 2–7. A lengthwise slot 501 traversingthrough the annular grooves 224 may then be machined into the MR dampervalve 223 as shown in FIG. 5. After the MR damper valve 223 has beenmachined, the slot 501 can be deburred to prevent damage to the coilwindings 300. According to one exemplary method, the MR damper valve 223may be heat treated to soften the material and improve the magneticproperties of the MR damper valve 223.

According to one exemplary heat treating method of the presentinvention, the MR damper valve 223 is heat charged in a wet hydrogenatmosphere with a dew point of approximately 75° F. (24° C.) to atemperature of no more than 1740° F. (950° C.) for approximately two toapproximately four hours. In another exemplary heat treating method ofthe present invention, the MR damper valve 223 may be heat charged in ain a wet hydrogen atmosphere with a dew point of approximately 75° F.(24° C.) to 1562° F. (850° C.). The MR damper valve 223 is then cooledat a rate of 180/306° F. (100/170° C.) per hour to 1000° F. (540° C.).Thereafter, the MR damper valve 223 may be cooled at any rate. In otherexemplary methods, different atmospheres such as, but not limited to,pack anneal, vacuum, dry hydrogen, argon, forming gas (comprisinghydrogen and nitrogen) may be used with a treating temperature in the1350/2150° F. (730/1180° C.) range.

According to one exemplary method of the present invention, the MRdamper valve 223 is placed in a jig fabricated for winding the coils300. A length of wire 1000 is then wound around each annular groove 224as shown in FIGS. 10–11. In one exemplary method, the wire 1000 istightly wound approximately 40 to approximately 60 times in each annulargroove 224. As those skilled in the art will appreciate, the number ofwindings may vary depending upon the desired magnetic field.Additionally, the coil windings 300 in each adjacent annular groove 224is wound in alternate directions. For example, if a first coil winding300 is wound in a clockwise direction, the adjacent coil winding 300 iswound in a counter-clockwise direction. In an alternate method of thepresent invention, the coil windings 300 may be wound in the samedirection.

In yet another exemplary method, thin strips of fiberglass matting (notshown) may be used to wrap coil winding 300 in each annular groove 224each coil segment. In another exemplary embodiment, gap plugs 227 may beinserted and secured within the lengthwise 501 between each coil winding300 prior to casting the coil windings 300 in a protective coating 301.In order to maintain flexibility of the wires 1000 that exit the MRdamper valve 223, silicon rubber (not shown) may be used to seal thecavities surrounding the wires. The end faces of the MR damper valve223, the inner bore of the damper valve 223, and the ends of the wires1000 can be waxed with mold release to prevent the coating 301 fromadhering to these parts during the casting process.

The MR damper valve 223 is then sealed within a mold 1900 (one half ofthe mold 1900 is shown in FIG. 19). The edges of the mold 1900 and themold breaking holes 1901 are sealed with high temperature tape (notshown). Prior to the introduction of the epoxy into the mold, the dampervalve-mold assembly may be heated to approximately 140° F. forapproximately 2 hours. A vacuum is applied to the damper valve-moldassembly and the epoxy to remove as much air from the epoxy and thedamper valve 223. The epoxy is then drawn through mold 1900 and a vacuummay then applied to further remove any air from the epoxy. The epoxy isthen allowed to pre-cure for approximately 12 hours. Thereafter; thedamper valve-mold assembly is heat cycled for approximately 26 hours andallowed to cool. The damper valve 223 is then removed from the mold 1900and any unwanted epoxy that has adhered to the surfaces of the dampervalve 223 can be removed. The completed damper valve 223 may be thencoupled to a piston end 220 and a damper rod 108. Alternatively, thecompleted damper valve 223 may be coupled to a reservoir gland 104.

According to another exemplary method of the present invention, thepolymer coating 301 can be applied to the coil windings 300 by a dipcoating process. The preparation of the damper valve 223 is similar tothe casting method with the exception to the process of coating the coilwindings 300. After the damper valve 223 has been assembled, hightemperature “flash breaker” tape (not shown) is applied over the coilwindings 300 to protect the coil windings 300 during the maskingprocess. According to one exemplary method, the flash breaker tapeshould be able to withstand at least 350° F.

After the coil windings 300 are taped, masking material is heated into aliquid state. According to one exemplary embodiment, McMaster CarrSupply masking material #7762T76 is used. As those skilled in the artwill appreciate, any masking material known or developed in the art maybe used in the dip coating process. According to one exemplary method, aportion of the damper valve 223 is dipped within the heated maskingmaterials. In another exemplary method, the ends of the damper valve 223are dipped within the heated masking materials. In yet another exemplarymethod, the whole damper valve 223 is dipped within the heated maskingmaterials. In another exemplary method, the masked damper valve 223 maybe subsequently heated to enhance the bonding between the damper valve223 and the masking material.

Once the masking material has been applied to the damper valve 223, the“flash breaker” tape (not shown) is removed from the coil windings 300.The damper valve 223 is then hung within a dipping chamber (not shown).The dipping chamber is then sealed and vacuumed to remove as much airfrom dipping chamber. The vacuum is run until air bubbles cease to breakout of the epoxy. Once the air has been removed from the chamber, thedamper valve 223 is submerged within the epoxy for approximately onehour. The vacuum is then slowly reduced, and the damper valve 223 isremoved from the epoxy when the epoxy begins to thicken. The epoxy onthe damper valve 223 is allowed to pre-cure for approximately 12 hoursat room temperature. The damper valve 223 then undergoes heat cycling tocure the epoxy and remove the masking material. Optionally, any unwantedepoxy may be cleaned from the damper valve 223. Once cleaned, thecomplete damper valve 223 may be coupled to a piston end 220 and adamper rod 108. Alternatively, the completed damper valve 223 may becoupled to a reservoir gland 104.

In closing, it is to be understood that the exemplary embodiments of thepresent invention disclosed herein are illustrative of the principles ofthe present invention. Other modifications that may be employed arewithin the scope of the invention. Thus, by way of example, but not oflimitation, alternative configurations of the present invention may beutilized in accordance with the teachings herein. Accordingly, thedrawings and description are illustrative and not intended to be alimitation thereof.

1. A vibration damping system comprising: a main housing having amagnetorheological damper valve movable within said main housing; areservoir chamber having a magnetorheological electromagnet, saidmagnetorheological electromagnet selectively energizable to adjust aprecharge pressure in said system; said main housing and said reservoirbeing in fluid communication with each other with a magnetorheologicalfluid; a control system; said control system including routines forselectively energizing said magnetorheological damper valve and saidmagnetorheological electromagnet so as to provide damping in saiddamping system over substantially the entire operating range of saiddamper system; said control system further including an electricalcurrent converter providing electrical current to saidmagnetorheological damper valve and said magnetorheologicalelectromagnet based on a variable frequency oscillation of saidconverter between a conduction phase and a regeneration phase.
 2. Adamper system according to claim 1, wherein said control system is anopen loop system.
 3. A damper system according to claim 1, wherein saidcontrol system is a closed loop system.
 4. A damper system according toclaim 1, wherein said main housing and said reservoir chamber areintegral.
 5. A damper system according to claim 1, wherein saidreservoir chamber includes a pressurized subchamber for exerting aninternal precharge pressure in said damper system.
 6. A damper systemaccording to claim 5, wherein said pressurized subchamber contains aninert gas.
 7. A damper system according to claim 1, further including awiper disposed on said magnetorheological damper valve, said wiper beingsized and shaped to substantially prevent said magnetorheological fluidfrom degrading seals in said system.
 8. The damper system of claim 1,wherein said system is disposed in a vehicle.
 9. The damper system ofclaim 8, wherein said system is disposed in a seat.
 10. The dampersystem of claim 1, wherein said system is disposed in a building fordamping seismic loads.
 11. A method of damping forces comprising:providing a magnetorheological (MR) damping system on a structureencountering periodic external forces, said damping system having amovable electromagnet and a stationary electromagnet, both of whichbeing in fluid communication with magnetorheological fluid; sensing atleast one external motion variable on said structure that cause movementof said movable electromagnet; selectively energizing one or both ofsaid movable electromagnet and said stationary electromagnet in responseto said sensed external motion variable so as to dampen movement of saidstructure over a wide operating range; said energizing being performedby introducing electrical current to one or both of said movableelectromagnet and said stationary electromagnet based on a variablefrequency oscillation of a converter between a conduction output phaseof said converter and a regeneration output phase of said converter. 12.The method of claim 11, wherein said magnetorheological damping systemis provided on a vehicle.
 13. The method of claim 11, wherein saidmagnetorheological damping system is provided on a building.
 14. Themethod of claim 11, further including sensing the temperature of saidmagnetorheological fluid prior to energizing one of said movableelectromagnet and said stationary electromagnet.
 15. The method of claim11, wherein said energizing of said movable electromagnet and saidstationary magnet is performed using a closed loop control system. 16.The method of claim 11, wherein said energizing of said movableelectromagnet and said stationary magnet is performed using an open loopcontrol system.
 17. A vibration damping system comprising: a mainhousing having a magnetorheological damper valve movable within saidmain housing; a reservoir chamber having a magnetorheologicalelectromagnet, said magnetorheological electromagnet selectivelyenergizable to adjust a precharge pressure in said system, wherein saidreservoir chamber includes a pressurized subchamber for exerting aninternal precharge pressure in said damper system; said main housing andsaid reservoir being in fluid communication with each other with amagnetorheological fluid; a control system; said control systemincluding routines for selectively energizing said magnetorheologicaldamper valve and said magnetorheological electromagnet so as to providedamping in said damping system over substantially the entire operatingrange of said damper system; said control system further including anelectrical current converter providing electrical current to saidmagnetorheological damper valve and said magnetorheologicalelectromagnet based on an oscillation of said converter between aconduction phase and a regeneration phase.
 18. A damper system accordingto claim 17, wherein said control system is an open loop system.
 19. Adamper system according to claim 17, wherein said control system is aclosed loop system.
 20. A damper system according to claim 17, whereinsaid main housing and said reservoir chamber are integral.
 21. A dampersystem according to claim 17, wherein said pressurized subchambercontains an inert gas.
 22. A damper system according to claim 17,further including a wiper disposed on said magnetorheological dampervalve, said wiper being sized and shaped to substantially prevent saidmagnetorheological fluid from degrading seals in said system.
 23. Thedamper system of claim 17, wherein said system is disposed in a vehicle.24. The damper system of claim 23, wherein said system is disposed in aseat.
 25. The damper system of claim 17, wherein said system is disposedin a building for damping seismic loads.
 26. A vibration damping systemcomprising: a housing having a magnetorheological damper valve withinsaid main housing; a control system; said control system includingroutines for selectively energizing said magnetorheological damper valveso as to provide damping in said damping system over substantially theentire operating range of said damper system; said control systemfurther including an electrical current converter providing electricalcurrent to said magnetorheological damper valve based on a variablefrequency oscillation of said converter between a conduction phase and aregeneration phase.
 27. A damper system according to claim 26, whereinsaid control system is an open loop system.
 28. A damper systemaccording to claim 26, wherein said control system is a closed loopsystem.
 29. The damper system of claim 26, wherein said system isdisposed in a vehicle.
 30. The damper system of claim 26, wherein saidsystem is disposed in a building for damping seismic loads.